1. Field of Invention
The present invention relates to a charger circuit, and particularly to a charger circuit capable of shifting to a low charging current after a predetermined maximum charging period is reached.
2. Description of Related Art
When a battery is being charged, whether to stop charging or not is usually determined by detecting if the battery voltage reaches a predetermined voltage. Yet, if the battery is dead, the battery voltage will never reach the predetermined voltage and the charger will be charging forever. Therefore, the prior art further provides a timer, such that the charging current is stopped when a predetermined maximum charging period is reached. The battery may be charged by a constant current or a variable current. U.S. Pat. No. 6,922,039 discloses a method for counting a charging time of a variable charging current, wherein the charging current is stopped when a predetermined maximum charging period is reached.
However, if the battery is a poor battery but not dead, that is, it is charged by a low rate for certain reasons but is not completely damaged, the poor battery which is still usable will be determined dead and is no more charged by the foregoing prior art.